The overall objective of this research is to develop a sensor for continuous in vivo monitoring of the blood glucose levels in diabetic patients. Our initial objective is to have a sensor capable of 3-4 days operation in hospitalized patients. The longer range objective is to interface the sensor with a feedback controller for an implantable insulin delivery system. Mechanistic studies were done using glucose oxidase and catalase entrapped in polyacrylamide gel embedded in a plantinum screen. This electrode, with reference to Ag/AgCl, gave potentiometric readings which were directly proportional to the logarithm of the glucose concentration of 10-250 mg glucose/100 ml. An alternative method of enzyme immobilization used glutaraldehyde to chemically crosslink the enzyme around 3-5 mm in length of 0.010 inch diameter platinum wire. This glutaraldehyde enzyme electrode exhibited similar basic response to that of the polyacrylamide gel electrode. Future research includes: (a) to complete the mechanistic studies of the sensor; (b) to define the sensitivity, rate of response limitation, etc. of the glutaraldehyde glucose sensor; (c) to fabricate a practical sensor and perform in vitro testing based on the enzyme-wire sensor and (d) to perform in vivo testing of the sensor in baboons.